Geomorphology of the Mirador-Calakmul Karst Basin: A GIS-based approach to hydrogeologic mapping.

This paper classifies the karst landscapes of the Petén Plateau and defines the Mirador-Calakmul Karst Basin by illustrating the distribution of its karst hydrologic features. Archaeological and spatial research of the Mirador-Calakmul area of Guatemala and Mexico has shown it to be a karst basin with geopolitical implications. Current research characterizes the karst landscapes of the Petén Plateau, maps the distribution of karst hydrologic features, and delineates the basin in geomorphological terms.

Exercise capacity after heart transplantation: influence of donor and recipient characteristics.

Background: For incompletely understood reasons, cardiac transplant recipients achieve only 60% to 70% of predicted values for maximal exercise capacity. The objective was to determine the characteristics of cardiac transplant recipients that are predictive of exercise capacity.

Methods: One hundred ten patients underwent maximal exercise testing using a modified Naughton protocol 26 +/- 1 months after transplantation.

Methotrexate for rejection prophylaxis after heart transplantation.

Background: The addition of vincristine to "quadruple-drug" induction immunotherapy (OKT3, cyclosporine, azathioprine, prednisone) after heart transplantation decreases the incidence of rejection but is limited by neurotoxicity. We hypothesized that methotrexate, when added to quadruple therapy, may also decrease the incidence of rejection but with less toxicity.

Methods: We randomized 36 heart transplant recipients to receive either quadruple therapy (OKT3, cyclosporine, azathioprine, corticosteroids) (n = 19) or quadruple therapy plus methotrexate (n = 17).

Effects of alloimmune injury on contraction and relaxation in cultured myocytes and intact cardiac allografts.

Objectives: This study was performed to determine the mechanisms by which allosensitized lymphocytes cause contractile dysfunction in cultured ventricular myocytes and to compare the effects on isolated myocytes with those observed in an intact heart preparation during allograft rejection.

Background: Allograft rejection may be associated with reversible abnormalities of both systolic and diastolic function. The immunologic mechanisms that cause ventricular dysfunction are poorly understood.